Previous studies by our laboratory and others have showed that chronic lymphocytic leukemia (CLL) cells exhibit elevated ROS generation, and that this oxidative stress renders the leukemia cell highly dependent on cellular antioxidant systems such as glutathione (GSH) to maintain redox balance and cell viability. Our recent study further showed that CLL cells were highly dependent on the bone marrow stromal cells to alleviate oxidative stress and promote their survival and drug resistance through enhancing GSH synthesis mediated by an intercellular metabolic communication involving cystine cysteine conversion and shuttling between the two cell compartments. These research findings provide new mechanistic insights into the biochemical interaction between leukemia and stromal cells. Importantly, the dependency of CLL cells on stromal cells for redox balance and cell survival has revealed an Achilles heel of CLL cells that can be targeted for therapeutic purpose. The main goal of this research project is to test the hypothesis that the metabolic communication between bone marrow stromal cells and CLL cells in cystine/cysteine/GSH metabolism can be used as a novel mechanism to selectively kill the leukemia cells using agents that preferentially impact the leukemia cells in the stromal environment. We propose to investigate the three Specific Aims: (1) Develop a novel mechanism- based therapeutic strategy to utilize the stromal-CLL intercellular interaction in cystine cysteine GSH metabolism as a unique pathway to convert the cystine analogs to toxic metabolites capable of selectively killing leukemia cells in the stromal microenvironment. (2) Investigate the high therapeutic selectivity of the cystine analogs that preferentially targets CLL cells in the presence of stromal cells, and exam the underlying mechanisms. (3) Use several CLL mouse models to test the in vivo therapeutic activity of the novel agents that by hijacking the stromal-CLL intercellular metabolic pathway to effectively kill CLL cells in the stromal microenvironment in vivo. Significance: This study will significantly advance our understating of leukemia-stromal interaction at biochemical levels and the role of such intercellular metabolic communication in leukemia cell survival and drug resistance. This study will also lead to the development of novel therapeutic strategies to effectively kill CLL in stromal microenvironment in vivo. Currently there is no effective therapy to overcome CLL drug resistance caused by the protective stromal microenvironment. The propose study will fill this significant gap by developing a novel strategy to turns the protective stromal cells into a metabolic machinery that produces active metabolite to selectively kill leukemia cells in tissue microenvironment, and thus will have important therapeutic implications in clinical treatment of CLL patients.